Regulation of binding of subfragment 1 in isolated rigor myofibrils.
J Cell Biol
; 111(6 Pt 2): 2989-3001, 1990 Dec.
Article
en En
| MEDLINE
| ID: mdl-2148565
ABSTRACT
A steric-hindrance model has been used to explain the regulation of muscle contraction by tropomyosin-troponin complex. The regulation of binding was studied by microscopic observation of mixtures of fluorescent subfragment 1 (S1) with rigor myofibrils at different actin-to-S1 ratios and in the presence and absence of calcium. Procedures were adapted to protect the critical thiols of S1 before conjugation to thiol-specific fluorochromes, this giving fluorescent S1 with unaltered enzyme activity. S1 binding was greatest in the I band (except at the Z-lines) in the presence of calcium regardless of the [S1]. The patterns in the absence of calcium depended on the actin-to-S1 ratios low [S1], binding in the myosin-actin overlap region; intermediate [S1], highest binding at the A-I junction; high [S1], greatest binding in the I-band. The two distinct binding patterns observed at low [S1] were demonstrated by dual-channel fluorescence microscopy when myofibrils were sequentially incubated with fluorescent S1 without calcium followed by a different fluorescent S1 with calcium. These observations support the concept of rigor activation of actin sites. The change in the pattern upon increasing [S1] without calcium demonstrate cooperative interactions along the thin filament. However, these interactions (under the conditions used without calcium) do not appear to extend over greater than 2-3 tropomyosin-troponin-7 actin functional units.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Subfragmentos de Miosina
/
Contracción Muscular
/
Miofibrillas
Tipo de estudio:
Prognostic_studies
Límite:
Animals
Idioma:
En
Revista:
J Cell Biol
Año:
1990
Tipo del documento:
Article